Compaq Parallel Database Cluster Model PDC/O2000 for Oracle8i and Windows 2000 Administrator Guide

Cluster Architecture 2-5
RA4000 Array Controllers
To ensure redundant I/O paths, two single-port RA4000 Array Controllers are
installed in each RA4000 Array or RA4100 Array. Only one array controller
can be active at any given time. One array controller is configured as the
active controller, and the other is the standby controller. To ensure fault
tolerance of shared storage on the RA4000 Array or RA4100 Array, the two
array controllers must be connected to a different Storage Hub, FC-AL Switch,
or Fibre Channel SAN Switch.
From the perspective of the cluster nodes, each RA4000 Array Controller is
simply another device connected to one of the cluster’s I/O paths.
Consequently, each node sends its I/O requests to the active RA4000 Array
Controller just as it would to any SCSI device. The RA4000 Array Controller
receives the I/O requests from the nodes and directs them to the shared storage
disks to which it has been configured. Because the array controller processes
the I/O requests, the cluster nodes are not burdened with the I/O processing
tasks associated with reading and writing data to multiple shared storage
devices.
When an RA4000/RA4100 Array and the cluster nodes to which it is
physically connected are first powered on, the RA4000/RA4100 Array
communicates with the nodes to identify which of its two array controller slots
contains the active array controller. The array controller that is installed in the
active slot is automatically assigned active status by Compaq Secure Path,
without the need for any further configuration. To determine which of the two
array controllers in an RA4000/RA4100 Array is currently active, find the
controller on which the ninth green LED is lit; this LED identifies the active
array controller.
To change the active slot location, use Secure Path Manager to make the array
controller in the other slot the active controller. For information about
configuring the standby array controller to be active, refer to “Defining Active
Array Controllers” in Chapter 5, “Installation and Configuration.”
If the active RA4000 Array Controller in an RA4000/RA4100 Array fails,
Secure Path causes the standby controller to become the active array
controller.